Generally, the usefulness of a given wire guide can be judged based upon several performance and dimensional characteristics. Often these performance and dimensional characteristics are mutually contradictory. For instance, one characteristic that is desired in all wire guides is pushability or kink resistance. However, it is also desirable that the wire guide have good flexibility characteristics, especially at its distal end so that the guide can adapt to curved passageways in a patient without causing potential trauma by possibly puncturing a vessel wall. It is often necessary to sacrifice one performance characteristic in favor of another when constructing wire guides due to inherent limits of the metallic materials usually used for making wire guides.
Another important characteristic of wire guides is often referred to as its torque-ability or steerability. This characteristic refers to the ability of the wire guide to transfer a torque in a one-to-one relationship from the proximal end to the distal end of the wire guide without a whipping effect caused by a torque build-up in the wire guide. Depending upon the materials used to construct the wire guide shaft, the above three characteristics are all coupled to one extent or another. In other words, an increase in torque-ability of a given wire guide often results in decreased flexibility and/or pushability in the wire guide.
One dimensional characteristic that is intimately related to the above performance characteristics is the diameter of the wire guide. It is usually always desirable to have the smallest possible diameter for the wire guide. However, most if not all materials used to construct wire guides have thresholds below which the diameter of the wire guide cannot be decreased without completely sacrificing one or more of the guide's performance characteristics.
What is needed is a compositely constructed wire guide shaft which affords some independent control over the various performance and dimensional characteristics of the wire guide to an extent previously not possible with the materials and structures taught in wire guides of the prior art.